1. Field of the Invention
The present invention relates to a recording material which enables monochrome or multi-color recording by utilizing pressure, light or heat and, in particular, it relates to a recording material which can reduce rippling of whole film caused by heat and waving of film edges caused by moisture.
2. Prior Art
Various recording methods utilizing light energy, heat energy and pressure in combination have been used for facsimile machines, various printers and the like. Recording materials used for these methods have an image-forming layer composed of a layer containing a coloring agent such as diazo compounds and lueco dyes, a layer containing a substance reacting with the coloring agent to develop color (color developing agent) and an intermediate layer separating the layers, the image-forming layer being provided on a support such as paper sheets and plastic films. In these materials, by encapsulating either of the coloring agent or the color developing agent in microcapsules which can be broken by pressure or in microcapsules which are composed of separator membranes showing extremely low permeability at room temperature but showing increased permeability under heating, the coloring agent and the color developing agent may be exist in the same layer and hence extremely wide variety of coloring agents can be used. Thus, those materials used for multi-color image-forming methods are produced at present.
As such recording materials utilizing the coloring agent and the color developing agent, there have been pressure sensitive paper and heat sensitive paper having layers each containing each of those agents separated by a separator layer and those containing the coloring agent and the color developing agent either of which is encapsulated in microcapsules. In these papers, the coloring agent and the color developing agent are separated from each other by separator layers or microcapsules walls and they are broken by pressurizing by typewriters or ball-point pens or by heating thermal heads to cause the reaction of the coloring agent and the color developing agent. There has also been heat sensitive paper where a colored layer containing the coloring agent and the color developing agent is decolorized by heating with a thermal head to typewrite characters.
As recording materials utilizing diazo compounds, there have been light and heat sensitive paper comprising a diazo compound, a coupler and a base in the same layer, the diazo compound being encapsulated in microcapsules showing no permeability at room temperature so that the diazo compound, the coupler and the base are prevented from causing reaction at room temperature. Such materials are heated image-wise with thermal heads or the like to increase permeability of the microcapsules so that the reaction of the diazo compound and the coupler and hence color development may be occur, and the diazo compound in non-image areas are inactivated by light exposure.
Further, as recording materials utilizing leuco dyes, there have been light and heat sensitive paper comprising, in the same layer, a leuco dye and a photo-oxidizing agent either of which is encapsulated in microcapsules, like those utilizing the diazo compound mentioned above. Such materials are exposed to light image-wise to cause the reaction of the leuco dye and the photo-oxidizing agent and color development, and the photo-oxidizing agent in non-image areas is made react with a reducing agent and inactivated by heating.
Furthermore, as recording materials utilizing photo-curing reaction, there has been light and heat sensitive paper comprising, in the same layer, a coloring agent, a photo-curing agent and a color developing agent, the coloring agent and the photo-curing agent being encapsulated in microcapsules so that these agent cannot cause reaction at room temperature. In these materials, the photo-curing agent in non-image areas is cured by light exposure and thereafter the color developing agent and the photo-curing agent are made react with each other by heating to develop color, i.e., to form images.
Recording materials utilizing paper sheets as their supports do not show marked deformation on heating for forming images. However, recording materials utilizing plastic sheets as their supports are likely to show deformation because plastic films generally have a relatively low heat deformation temperature. For example, polyester, which is the most commercially popular plastic material for the support, has a glass transition temperature of about 70.degree. C. and, if a plastic film composed of it is employed for a use where it is heated to a temperature above its glass transition temperature, the film would be softened and hence deformed. When recording materials utilizing plastic films as supports are used as printing sheets, the materials are deformed due to heating and they are given a very wavy form as a whole. Such phenomena are particularly remarkable in machines using a high temperature and, in such machines, the sheets would cause jamming in the sheet transfer route.
Therefore, plastic films can be used for such purpose only in machines using a low image-forming temperature and a short heating time and machines using a high heating temperature cannot use materials utilizing plastic films as supports, but only those utilizing paper sheets.
Further, recording materials comprising plastic films are usually cut into sheets and stacked or rolled for their storage. The films stored in the form of stacked sheets or rolled film absorb moisture from four edge sides in the case of stacked sheets and from both ends of roll in the case of rolled sheets and they exhibit wavy edges (so-called "petal phenomenon") when they are spread or unrolled.
As a method for preventing the petal phenomenon, humidity controlling paper sheets containing a controlled amount of moisture have been interleaved between adjacent films to reduce the influence of outside air humidity. In this method, the additional process step for interleaving the humidity controlling paper sheets is inevitable and the paper sheets must be pealed and discarded upon use of the films. These steps make the process troublesome and may cause problems from the viewpoint of resource-saving.
The object of the present invention is to solve the above problems and to provide a recording material less susceptible to waving of the whole film caused by heat and edge waving caused by moisture. A further object of the present invention is to provide recording material which retains flat form and does not cause jamming even when it is used in machines utilizing a high heating temperature, and in which the petal phenomenon caused by moisture absorption upon its storage is prevented.